With Tiger Woods, and other Type-A guys having multiple sex partners extra-marital, science can actually help explain much of the cheating behavior. Multiple sex partners is sex addiction, caused primarily by a born deficit in the brains dopamine reward system….this creates lifetime brains that feel they’re “starving.”

The Loving Landscape This can be a long topic but I’ll keep it short here. Let’s do a reality check. The divorce rate is 3+%, NOT 50%. The rate of extra-marital sexual affairs is about < 7%. Stats are hard to find but it's very low. Don't be mislead by Desperate Housewives or other pop media. Not sure why we like to keep the 50% divorce stat illusion but it must serve some purpose since it has not been actively disproved.

However extra-marital sex is a hot pop media topic because it seems to be more prevalent in public personalities and there are brain reasons for this. Tiger Woods and ploiticians being the latest. It is also a hot topic because the idea that a man would abandon his children is a big fear trigger.

Bottomline, it is an addiction like the rest. This is a very shorthand description and no substitute for real brain scientists chiming in. This is all old research BTW.

Driven by Dopamine Dopamine is the key. Dopamine is the main “feel-good” neurotransmitter that evolved to direct mainly muscular movement and feeding. Think of the brain constantly, largely unconsciously, scanning the environment to identify the best food cues, then directing our limbs and muscles in those directions. The dopamine system is so critical it literally sits atop the brain stem, “directing” sensory input to and from the rest of the nervous system and sensory inputs.

The normal brain has a balanced and complete dopamine receptor system. This brain has a pretty easy time staying relaxed, enjoying life with minimal energy exertion in mind or body, and when needed triggering appropriate, well-targeted, goal-directed behavior when it needs to feed. The system is so efficient and robust, the dopamine system has been carried over to other enjoyable activities and “food-like” rewards. You know the list. Most businesses are built on satisfying dopamine needs quickly and cheaply. Likely driving and TV watching are dopamine triggering in a normal range.

The Brain Born Starving For a small, but very active and visible, few however (let’s set gender differences aside for this article) they are born with fewer than normal dopamine receptors. This is NOT good. This causes all sorts of problems with what should be the normal brain system for taking care of one’s most basic needs. Remember: food.

This effects all areas of ones life but let’s stick here with love relationships.

Since it doesn’t have the normal amount of dopamine receptors, this brain is always in a state of “starvation.” It’s called a “reward deficit disorder.” Symptoms start early in twitchy, agitated behaviors. Impulsive behavior in children, often mirrors the same in their parents who have the same constantly craving brains. Bad combination.

These brains cannot rest or find peace. They have a chronic and acute state of feeling uncomfortable and being triggered to search to calm that discomfort. Sadly, even though these brains et the least rest, they have to expend far more energy than the rest of us to just get through each day.

Generally any extreme or high energy activity, including mental activity, triggers extra dopamine. But the extra dopamine doesn’t help since these brains have a much more limited capacity to take in dopamine to begin with. Flooding the system with extra helps…but only for the moment.

If you had a car with a 1 galleon gas tank think of how hard, distracted, agitated and exhausting driving would be. You would ALWAYs have to be finding a gas station and filling up. Always on edge. Overflowing the 1 galleon gas tank wouldn’t help and , in fact, would just create a dangerous, flammable risk. Every time.

Acting the Dope There are a lot of implications and additional interesting issues around this kind of brain but let’s stay laser-focused on how this brain goes bad in love.

Here I’ll reference two Nature papers, sorry I don’t have the digital links or access. If I did, I would cut and paste. They are listed below. They studied prairie voles which are, sometimes, monogamous rats. FYI, our basic brain systems evolved millions of years ago and are the same in structure and function from mammals, other social animals and monkeys. The rat brain works just fine to study our basic mating behavior. FYI – 3%-5% of mammals have monogamous relationships : “pair bonding.”

This is a much more complicated process then sketched out here and the full article goes into details.

Two dopamine receptors seem important: D2 and D1. They work in tandem and a one-two punch is needed for the pair bond to form and last.

D2, sets up partner preference after spending time with a love object. Mating increases D2 activation and density.

I will forgo for here describing the different areas of the brain involved in this behavior. It is spread out across the basic reward centers. Overall, mating increases dopamine about 50% in males and females.

It is likely that males that cannot form pair-bonds, that “cheat” suffer from a lack of the D2 receptors or disorder. Without the D2 receptors working, the male brain ends up in a compulsive chase to mate/pair-bond with different females. But since the receptors aren’t working, the mating never “takes.” Like being starving and eating but never feeling full. Tragic.

These are not bad people, they are likely good people with a bad brain disorder.

Note: Can we really use rat brain as proxies for ours? Sure “Of Mice and Men Just how closely must mouse models replicate the known features of human disorders to be accepted as useful for mechanistic and therapeutic studies? Soliman et al. (p. 863, published online 14 January) compared mice that vary only in their allelic composition at one position within the gene encoding brain-derived neurotrophic factor (BDNF) with humans exhibiting the same range of allelic variation. Individuals (mice and humans) carrying the allele that codes for a methionine-containing variant of BDNF retained a fearful response to a threatening stimulus even after its removal in comparison to those with the valine variant. Furthermore, in both cases, this linkage was mediated by diminished activity in the ventral-medial region of the prefrontal cortex. This deficit in extinction learning may contribute to differential responses to extinction-based therapies for anxiety disorders.”